Project Summary Over the past two decades, we have seen a nationwide increase in the use of medical-legal partnerships (MLPs) to address health disparities affecting vulnerable populations. These partnerships increase medical teams' capacity to address social and environmental threats to patients' health, such as unsafe housing conditions, through partnership with legal professionals. Despite expansions in the use of MLP care models in hospitals and clinics, formative work to evaluate this approach and test its efficacy to promote HIV care and wellness among people living with HIV (PLWH) has yet to be conducted. Building on gaps in the current literature, we propose a mixed-methods study to develop an MLP-comprehensive HIV care diffusion model to build an understanding of avenues through which such partnerships can improve outcomes in the HIV care continuum. First, a national survey of 100 medical-legal partnership service providers from the existing 294 medical-legal partnership programs will be conducted to identify and assess existing best practices among current MLPs. Next, in-depth interviews with 50 dyad-based interviews of MLP service providers and HIV positive clients will be conducted to gauge the potential large-scale impact of legal partnerships on addressing legal problems, reducing legally-related psychosocial burdens, and improving outcomes in the HIV care continuum, including engagement in care and viral load suppression. We will then develop an MLP- comprehensive HIV care diffusion model and its benchmarks of success based on data grained through Aims 1 and 2. We will use Exploration, Preparation, Implementation, and Sustainment (EPIS) framework to develop an MLP-comprehensive HIV care diffusion model and its benchmarks of success to improve outcomes in the HIV care continuum. The model will be tested in a subsequent R34 submission using a Sequential Multiple Assignment Randomized Trial (SMART) design for evaluating adaptive interventions. The proposed study builds on the investigative team's experience with HIV Law research, as well as consultants' record of HIV research and experience with MLP implementation. To our knowledge, this study will be the first to examine the impact of MLPs on outcomes in the HIV care continuum. Rigorous methodology, including detailed documentation of quantitative and qualitative components, will ensure that this study may be scaled up and replicated in various communities to provide continuous support, integration of care, and protection for this heavily impacted group.